1. Field of the Invention
This invention relates to a magnetic disk used for a magnetic disk drive and, more particularly, to the texture configuration of the disk surface.
2. Description of the Prior Art
FIG. 4 shows a top view of a magnetic disk having a plurality of concentric streaks formed by a prior art process disclosed in Japanese Patent Disclosure 61-29,418, and FIG. 5 is an enlarged scale sectional view taken along line V--V in FIG. 4. In these Figures, reference numeral 1 designates a base, numeral 2 concentric streaks, numeral 3 a ground layer, numeral 4 a magnetic film, numeral 5 a protective film, and numeral 6 a lubricant film.
Usually, the magnetic disk of this type is formed as follows. The surface of the base 1 is polished, and the polished surface is plated with a Ni-P alloy to form the ground layer 3, which is then polished. Subsequently, the ground layer 3 is formed with fine irregularities with a grinding tape or the like in order to prevent a head slider from sticking to the disk. These surface irregularities are formed as concentric traces or grooves which appear as streaks on the disk surface.
Afterwards, the magnetic film 4 for recording data therein is formed by means of sputtering on the ground layer 3. Then, a carbon or ceramic film is formed as the protective film 5 by means of sputtering on the magnetic film 4. Finally, the lubricant film 6 is formed on the protective film 5.
Recent magnetic disk drives adopt a commonly termed contact start-stop (CSS) system. In this system, a head slider is in contact with a magnetic disk while the disk is stationary, and when the disk starts to rotate, the head slider starts to float of the disk, sliding on the disk surface until the slider floats fully away from the disk surface.
As shown above, the prior art magnetic disk has concentric surface streaks. Therefore, in areas of the disk surface that are in contact with the head slider, edges of raised portions of the surface texture are formed substantially parallel to the length direction of the air-bearing surface of the head slider. This means that the disk surface area in point or line contact with the air-bearing surface of the head slider varies in the disk surface due to undulation or sinuosity of the edges, thus leading to great difference between the maximum and minimum values of dynamic friction measured over the entire circumference and unsteady torque at the time of the start of disk rotation.
In an ordinary disk drive, a plurality of magnetic disks are mounted at a time. Therefore, if all the disks are stopped at a position corresponding to the maximum value of the dynamic friction, a great torque is required at the time of start of the disk rotation. In addition, it is liable that the head slider fails to float above the disk normally, resulting in a headcrash.